In medical practice, it is common to obtain a sample of a fluid for evaluation of various characteristics to aid in evaluation of a patient's health. Examples of such fluids include blood, urine, and stomach contents, which may be taken for analysis. Characteristics of the fluids that may be measured include pH and the presence or levels of various chemicals or medication. Fluids may be taken as a diagnostic aid and also to aid in placement of medical devices such as medical tubing for feeding, breathing, medication, and other uses.
There are many different clinical situations in which it is beneficial to know the gastric pH of a patient, or other chemical properties associated with the patient. Currently to determine the pH, a practitioner aspirates the stomach contents from a lumen (e.g., nasogastric tube, feeding tube, gastric tube) that is in communication with the stomach into a syringe. The contents are then expelled from the syringe and placed in a test tube and sent to a lab for a gastric pH analysis. It is also possible to place a pH probe down the lumen to attain a reading of the stomach contents. However these methods take a considerable amount of time and both can be costly. Another method is to aspirate the stomach contents into the syringe and then expel the contents of the syringe onto litmus paper or other pH indicating paper. This method is also timely and forces the practitioner to handle bodily fluids in the open. This can be both messy and inaccurate.
The pH is measured for multiple reasons. The most common reason being to monitor an intubated or critically ill patient's gastric pH. This is often measured because these critically ill patients develop gastric ulcers due to a lower gastric pH. These ulcers can bleed rapidly and are a cause for significant morbidity and mortality. These often require emergent endoscopy and cauterization to stop the bleeding.
Patients that are critically ill are often on medications that raise the gastric pH. However, dosages needed to adequately raise the pH of the stomach in critically ill patients may vary for each patient and are difficult to determine without measuring the gastric pH. This is often not done because it can be timely and costly to do so. Deviation in gastric pH from a relatively narrow preferred range has been associated with higher risk for certain types of pneumonia, ulcers, gastric bleeding, and other complications.
Detection of the desired characteristic is typically shown using a visual indicator, such as a colorimetric medium that changes from a first color to a second color upon sufficient contact with the fluid. For example, determining the pH for a sample of stomach contents can be performed with a litmus paper which turns red or blue upon contact with acids or bases, respectively. However, some media produce a range of colors responsive to a range of pH values, which both enables the acquisition of a pH reading, and creates challenges for medical personnel in correctly performing, interpreting, and recording the measurement. In addition, the fact that the response of the colorimetric medium can vary from manufacturer to manufacturer, manufacturing lot to manufacturing lot, and other conditions, makes the reliable acquisition of an accurate reading even more challenging.
Determination of the characteristics is often performed by a practitioner (e.g., nurse or doctor) who views the colorimetric medium for the change to occur. However, with many indicator mediums, the initial color change may happen quickly and include a range of colors. For example, a pH paper may be designed to change colors between a range of blue, green, and brown or between red, orange, and yellow to indicate specific levels of pH. The practitioner must then compare the colors of the pH paper with a known reference color to estimate the pH value. Reference colors are often provided on a separate chart for comparison with the visual indicator. Determination of the characteristics generally must be performed without delay, as the sample pH may change when the sample is exposed to air, and the response of the colorimetric medium may be stable and accurate for only a limited time after the medium is exposed to the sample.
A further challenge in a clinical setting is avoidance of personnel exposure to gastric aspirate and other bodily fluids.